1. Field of the Invention
The invention concerns an electric machine with at least one primary part and at least one secondary part, in which the secondary part is moveable in relation to the primary part by the force of magnetic fields.
2. Description of Prior Art
Electric machines with high rpms, or if configured as linear direct drives, with high speeds of movement of primary parts in relation to secondary parts, are characterized by high power densities. In such machines, considerable losses are generated in the soft magnetic body.
If, besides high top speeds, large forces are required, a high peak output (P=v·F) is the result. It is known to reduce this peak output by means of field weakening at high rpms. Induction machines permit a simple realization of field weakening, however, in a full exciter field they achieve only approximately 70% of the surface thrust density of permanent magnet machines. On the other hand, the field regulating range in permanent magnet machines is limited and causes either considerable losses due to high field weakening currents in the primary part or requires an expensively constructed, hybrid excited secondary part.
From DE 28 02 753 C2 a synchronous machine with a magnetic field parallel to its axis is known, the soft magnetic body of which can consist of magnetic powder with an added binding agent. By turning two disk-shaped multiple pole multiple phase windings in opposite direction to each other in circumferential direction, weakening of the field is achieved.
From DE 41 37 457 C1 a permanent magnet generator is known, in which voltage is regulated by means of an adjustable screen made of a magnetically conducting material.
In DE 44 26 241 C2 an electric machine with permanent magnets in a collector arrangement is described, which is characterized by the configuration of its glue points.
In DE 35 36 583 A1 a transverse flux machine with permanent excitation is described, in which the winding consists of coils that utilize only a fraction of the circumference of the machine. Several soft iron elements are arranged within the coils with recesses between the soft iron elements at the air gap, the width of said recesses in direction of movement corresponding approximately to the width of the soft iron elements. Return of current occurs on the outside of the soft iron elements so that only a small part of the conductor length is contributing to the generation of power.
The objective of the present invention is therefore, to advance an electric machine for high magnetic reversal frequencies in such a manner, that high power density is achieved concurrently with low losses and that production expenditures remain low.